During the manufacture of many consumable products, sheet materials are subjected to an embossing process or to a bonding process in which the sheet materials are pressed against a rotating roll having a plurality of raised elements. The raised elements form densified areas in the sheet material which can be, for instance, embossments or bonding areas.
The sheet materials are subjected to a process as described above for various different reasons. For instance, in some embodiments, the sheet materials are embossed solely to improve the aesthetic appeal of the product. For instance, many tissue products, such as paper towels and bath tissues, are embossed with decorative designs.
In other embodiments, the sheet materials may comprise a plurality of layers and the densified areas are used to bond the different layers together. For instance, the different layers contained within the sheet material may be made from thermoplastic polymers that soften and form the bond areas when contacting the raised elements on the rotating roll. The layers contained within the sheet materials, for instance, may comprise nonwoven webs made from thermoplastic fibers and/or may comprise polymer films. In order to form the bond areas, typically some type of energy is needed to cause the thermoplastic materials to soften. For example, ultrasonic horns are sometimes used in combination with the rotating roller containing the raised elements in order to subject the sheet material to ultrasonic energy.
In an alternative embodiment, thermal energy is used in order to form the bond areas. In this embodiment, for example, the roller containing the raised elements may be heated using an electrical resistance heater or by circulating a hot fluid, such as an oil, through the roller.
In these types of processes, a reoccurring problem is that the raised elements on the rotating roller may have sharp edges that cause tearing, fracturing, fatiguing, or general weakening of the sheet material as the material is fed through the process. For example, the sharp edges may have a tendency to damage the sheet material as the sheet material contacts the leading edge of the raised element and as the sheet material contacts the trailing edge of the raised element. In some instances, for instance, edges on the raised element have been known to even form holes in the sheet material being processed.
In the past, various attempts have been made in order to minimize the effects of any edges present on the raised elements. For instance, the raised elements on the bonding roller have been mechanically worked in order to reduce sharp edges and to lessen the damage that may be caused by the raised elements. Such attempts, however, have not fully eradicated the problem and/or have added great cost in producing the equipment used to run the process. As such, further improvements are still desired.